Fuel Borne Catalysts for Sulfur Rich Fuels

ABSTRACT

Fuel Borne Catalysts of use in High Sulfur Fuels are disclosed, where formulations may include any number of suitable platinum group metals, transition metals, rare earth metals, and alkaline earth metals, including platinum, palladium, iron, manganese, cerium, yttrium, lithium, sodium, calcium, strontium, vanadium, silver and combinations thereof.

BACKGROUND

1. Field of the Disclosure

The present disclosure relates generally to fuel additives, and moreparticularly to fuel borne catalysts of use in high sulfur fuels.

2. Background information

Diesel engines are highly regarded for their efficiency and reliability.However, they may produce a level of pollution higher than that desired,and may need to have after-treatment strategies, including one or moreof either a catalyzed Diesel Particulate Filter (DPF) or DieselOxidation Catalyst (DOC)—to control Particulate Matter (PM), Hydrocarbon(HC), and Carbon Monoxide (CO) emissions. High sulfur concentrations inthe fuel may make some after-treatment devices ineffective due tofouling by sulfate and vigorous chemical attack by sulfur oxides on theDPF/DOC and the catalysts, as most active PGM catalysts for theseoxidation reactions typically also catalytically oxidize SO2 to SO3,which in conjunction with water vapor forms sulfuric acid. SO2 may alsocompete with oxidizable species for active sites on catalysts, and hencemay affect NO, CO, HC, and Carbon oxidation. This in turn may result inan increase of the temperature required for Diesel Particulate Filterregeneration and an increase in Balance Point Temperature.

As a result, a number of countries have mandated the use of Ultra LowSulfur Diesel (USLD). However, fuels containing sulfur levels of up to3000 ppm are still in use in various parts of the world—in some cases inspite of regulations to the contrary. These levels of sulfur may causeone or more of the aforementioned problems for after-treatment devicesof use in the reduction of Particulate Matter (PM) emissions, includingparticulate filters and diesel oxidation catalysts. Reasons for theseproblems may include the ability of catalysts to oxidize both NO to NO2,a desired reaction, and SO2 to SO3, an undesired reaction.

SUMMARY

The present disclosure relates to Fuel Borne Catalyst (FBC) formulationsof use with High Sulfur fuels, which may include platinum, palladium,iron, manganese, cerium, yttrium, lithium, sodium, calcium, strontium,vanadium, silver and combinations thereof.

LIST OF FIGURES

Embodiments of the present disclosure are described by way of examplewith reference to the accompanying figures, which are schematic and arenot intended to be drawn to scale. Unless indicated as representingprior art, the figures represent aspects of the present disclosure.

FIG. 1 is a Sulfur Conversion Efficiency Comparison Graph

FIG. 2 is a Backpressure Change Graph

FIG. 3 is a Backpressure Change Comparison Graph

DETAILED DESCRIPTION Definitions

As used herein, the following terms have the following definitions:

“Fuel Borne Catalyst (FBC)” refers to any material suitable for use as acatalyst able to be stored in fuel as one or more of a solute, colloid,or otherwise suspended material.

“Conversion” refers to the chemical alteration of at least one materialinto one or more other materials.

“Catalyst” refers to one or more materials that may be of use in theconversion of one or more other materials.

“High Sulfur Fuel” refers to fuel with a sulfur content of about 100 ppmor greater.

“Low Sulfur Fuel” refers to fuel with a sulfur content of about 50 ppmor fewer.

“Platinum Group Metals (PGMs)” refers to platinum, palladium, ruthenium,iridium, osmium, and rhodium.

DESCRIPTION OF THE DRAWINGS

Various example embodiments of the present disclosure are described morefully with reference to the accompanying drawings in which some exampleembodiments of the present disclosure are shown. In the drawings, thethicknesses of layers and regions may be exaggerated for clarity.Detailed illustrative embodiments of the present disclosure aredisclosed herein. However, specific structural and functional detailsdisclosed herein are merely representative for purposes of describingexample embodiments of the present disclosure. This disclosure however,may be embodied in many alternate forms and should not be construed aslimited to only the embodiments set forth herein.

Platinum and palladium compounds of use as Fuel Borne Catalysts (FBCs)include those described in U.S. Pat. No. 4,892,562; U.S. Pat. No.5,034,020; and U.S. Pat. No. 6,003,303. These include soaps,B-diketonates and alkyl and arylalkyl metal complexes. One or more ofsaid compounds may be suspended in fuel or may be fuel soluble and fuelstable at dose rates, including rates below 0.5 ppm metal and asdiscussed in the patents cited above.

Transition metals suitable for use in FBCs include iron, manganese,silver, and vanadium. These metals can be present in FBCs as anysuitable compound, including long chain carboxylate salts with carbonchain lengths of 5 to 20 carbon atoms or, for iron, as ferrocene andferrocene derivatives. Suitable forms of silver may include: fuelsoluble carboxylates, such as a long chain alkyl soap with 5-20 carbonatoms; a substituted benzoate salt with 10 or more carbon atoms,including a benzene ring; an acetylacetonate; and any suitablederivatives.

Forms of Vanadium suitable for incorporation as a fuel stable complexinclude various forms and oxidation states, such as VO(acac)₂ andderivatives, divalent V(cpd)₂ and derivatives, and V(OR₁)₂(R₂)₂(vanadium oxyalkyls and alkyls) where R contains at 4 or more carbonatoms and can be mixed oxyalkyl with alkyl or the alkyl or oxyalkyl maybe all the same as in V(R)₄. Vanadium soaps of +4 and +5 oxidationstates may also be of use, including amongst others V(OOCR)_(n), where Ris an alkyl group containing 5 or more carbon atoms and n is 4 or 5.

Other transition metals suitable for use in FBCs include one or morerare earth metals, such as cerium and yttrium, and may be employed inany suitable form, including those listed in patents cited in thisdisclosure. Suitable forms include one or more soaps, acetylacetonates,and the like.

Other suitable metals include Calcium, Strontium, Sodium, and Lithium.Calcium and strontium may be present in the FBC in any suitable form,including long chain soaps, M(OOCR)₂, where R contains at least 5 carbonatoms. Sodium and lithium may also be supplied as long chaincarboxylates with more than 9 carbon atoms.

These may combine with long chain polar co-solvents to increasestability of relatively more polar alkali metal compounds, such ascompounds of the type HOR₁OR₂OR₃, where R is alkyl. Suitable co-solventsof this type include diethylene glycol monobutyl ether. Other suitableco-solvents include ROH where R contains at least 6 carbons, octanol andother higher alcohols.

SO3 and H2SO4 Formation

In the absence of catalysts, about 1-2% of SO2 in the engine exhaust maybe converted to S03. High SO3 concentrations are favored by lowtemperatures. However, at low temperatures, the un-catalyzed reactionrates are insignificant-explaining why engine out SO3 is normally onlyabout 1% of total sulfur oxides. SO3 reacts exothermically with themoisture present in the exhaust to form sulfuric acid and other sulfatesthat may readily foul filter surfaces and may cause operationalproblems.

The exhaust gas of a typical diesel engine operating on a fuelcontaining 1000 ppm of Sulfur may contain 30 ppm of SO2 and about 0.3 to0.6 ppm of S03. Some catalysts, including those using Pt on Al203, mayincrease the SO2 oxidation rate to 50% or more at temperatures as low as250° C., which may result in over 15 ppm SO3 in the exhaust. SO2 mayalso compete with oxidizable species for active sites on catalysts, andhence may affect NO, CO, HC, and Carbon oxidation. This in turn mayresult in an increase of the temperature required for Diesel ParticulateFilter regeneration and an increase in Balance Point Temperature by asmany as 33° C., though these increases may stop once sulfurconcentrations in fuel reach 30 ppm or higher.

The use of similar metals in an FBC formulation may not induce theseeffects when the size of the catalyst particle is below about 40 nm.

FIG. 1 shows Sulfur Conversion Graph 100, showing the sulfur conversionefficiency of Platinum FBC 102, Catalyst A 104, Catalyst B 106, andCatalyst C 108, where Catalyst A 104, Catalyst B 106, and Catalyst C 108are PGM containing non-FBC catalysts and the fuel contains Sulfur at aconcentration of 500 ppm. Platinum FBC 102 shows a very low sulfurconversion efficiency up to 450° C., while Catalyst A 104, Catalyst B106, and Catalyst C 108 show a comparatively higher sulfur conversionefficiency at temperatures as low as 200° C.

SO2 may also diminish FBC PGM catalytic activity at concentrations above10 ppm, including concentrations between 10 ppm and 30 ppm. This mayresult in unreliable regeneration at low FBC concentrations in the fueland at moderate temperatures. Li2O2—formed by combustion—may partiallyalleviate the problem of SO2 deactivation by wetting the Pt crystallite.However, lithium may not be a very effective metal oxidization catalyst,and and auxiliary heat pre-filter may be routinely required.

FBC Formulations

FBC formulations of use with high sulfur fuel include formulationscontaining one or more of the following and combinations thereof:

-   -   A platinum group metal—including Pt or Pd—at 0.01 to 0.5 ppm in        the fuel    -   A transition metal—including Fe or Mn—at 1-10 ppm in the fuel    -   A rare earth metal—including Ce or Y—at 1-10 ppm in the fuel

Additional materials of use in the fuel include:

-   -   Li or Na at 0-3 ppm, which may be of use in activating the PGM        catalyst    -   Ca or Sr at 0-3 ppm, which may act as a sulfate sink    -   V at 0-3 ppm, which may modify SO3 formation    -   Ag at 0-3 ppm

FBCs including aforementioned materials may facilitate NO2 carbonoxidation mechanisms, while producing relatively small amounts of NO2 inthe exhaust when compared to other catalyst systems. The use of certainmetallic FBC components—including platinum, palladium and combinationsthereof—may provide negligible SO3 formation while maintaining carbonoxidation catalysis by nearest neighbor atom NO2 formation as describedbelow. At temperatures similar to those commonly found in DOCs and DPFs,these NO₂ enhanced oxidation reactions may dominate.

Increasing the concentration of NO2 in may be beneficial, since NO2 maybe a much more effective oxidizing agent than O2 for carbon-based PMsoot, Soot loading is one of the limiting factors in DPF operation.

When used in FBCs with no PGM content, transition metals including Mn,Fe, and Cu, may foul DPFs at the concentrations necessary. The additionof Na and Li additives to these types of FBC may allow regeneration attemperatures low enough to permit regeneration at high doses of metaland may show some promise in improving trap regeneration. However, COand HC reduction may not occur.

Methods suitable for enhancing DOC/FBC soot oxidation performance inhigh sulfur fuels include those functioning at the nanoscale level.These methods may not drive the bulk gas phase NO2 concentration tohundreds of ppm, but may instead enhance NO2 formation and reduce theill effects of sulfur oxides at the Platinum-Transition Metal Oxide-RareEarth Metal Oxide [Pt-TMO-REO] (or Platinum-Base Metal oxide [Pt-BMO])crystallite surface.

SO2 may temporarily inhibit the aforementioned mechanism by weakadsorption of SO2 on the nanoparticulate Pt-BMO complex. This mayincrease filter regeneration temperatures, which may be suitable ifoperating temperatures are suitably high. Suitable alkali metals,including sodium or lithium, may be used as part of the FBC tocontinuously wet the Pt/BMO crystallite with a suitable peroxide film,including Na2O2/Li2O2, to reduce this problem.

According to K. Krishna, M. Makkee, (“Pt—Ce-Soot generated from FuelBorne Catalysts: Soot Oxidation Mechanism”, Topics in Catalysis, 42-43,229-236 (2000)), the evidence is that nitrate rather than free NO₂itself is the most effective carbon oxidizer at the lowest temperaturesand that NO₂ complex formation is key to forming the C—ONO₂ (or theprecursors such as Pt-BM(NO₂)(O)) carbon-nitrate oxidation couple thatdirectly leads to carbon oxidation (and to some extent NO_(x) reduction)by this mechanism. The oxidation of soot may take place via theso-called surface oxygen complexes. For soot oxidation to proceedreadily, defects in the soot surface may be necessary. NO₂, andespecially nitrates, are very active surface defect initiators, and maythereby assist in the formation of surface oxygen complexes and theacceleration of soot oxidation. SO2 may be adsorbed by the Pt and Pt-BMOcrystallites in a weak surface association and inhibit the desiredoxidation sequence.

Fuel Borne Catalysts may promote soot oxidation at low temperatures.Close contact between the (Pt)-BM oxide nanostructure and the carbon mayallow the nitrate decomposition product to readily react with carbon inthe soot, thereby creating high efficiency defects in the carbon sootstructure.

FIG. 2 shows Reference FBC Backpressure Graph 200, showing the behaviorof a reference Pt FBC when used with Low Sulfur Fuel 202 and with HighSulfur Fuel 204. The decrease in average backpressure using Low SulfurFuel 202 in run 3-4 is indicative of regeneration, and is a behavior notshown by High Sulfur Fuel 204.

FIG. 3 shows Backpressure Comparison Graph 300, showing the behavior ofReference FBC with 15 ppm S 302, Reference FBC with 1000 ppm S 304, andHSF FBC with 1000 ppm S 306. As in FIG. 2, The decrease in averagebackpressure using Reference FBC with 15 ppm S 302 in run 3-4 isindicative of regeneration, and is a behavior not shown by Reference FBCwith 1000 ppm S 304. However, HSF FBC with 1000 ppm S 306 shows sign ofregeneration in run 2-3.

EXAMPLES Example 1

In this example, a comparison of the DPF backpressure characteristicsfor two FBC formulations is made. In this example, the Reference FBC isa bi-metallic formulation containing only platinum and cerium that mayvery effectively cause filter regeneration (also as noted in the charts)used in low sulfur fuel but may be ineffective in a High Sulfur fuelcontaining 1000 ppm Sulfur. In this example, the “HSF FBC” containsplatinum, cerium and iron with a similar amount of total metal, but theamount of metal corresponding to cerium in “Reference FBC” is insteadsplit between iron and cerium in “HSF FBC”. This use of this compositioncauses regeneration to occur with 1000 ppm S fuel under the same engineduty cycles (400 C exhaust temperature max), where the “reference”formulation failed.

Analysis of PM from these cycles indicate neither Reference FBC nor HSFFBC significantly generate SO3 or SO4 in high S fuel, as sulfate isbelow 10% of the PM for both cases by analysis and comparable tobaseline measurements and, in neither case, is the amount of FBC metalin the PM greater than the amount of lube oil metals that may benormally present. The difference in filter regeneration performance isnot due to the differences in total metal present or to differences insulfate in the PM, but due to a differing mechanism which may reduce theadverse effects on PM carbon oxidation catalysis caused by highconcentrations of SO2 in the exhaust when platinum, cerium and iron areall present, as compared to the reference case where similar amounts ofonly platinum and cerium are present.

I claim:
 1. A method of improving the operation of a diesel engineoperating with high sulfur fuel, the method comprising the steps of:providing for adding to a diesel fuel of a fuel borne catalyst in aneffective amount to lower the emissions of unburned hydrocarbons andcarbon monoxide, the fuel borne catalyst comprising: a platinum groupmetal composition comprising at least one material selected from thegroup consisting of platinum, and palladium, or mixtures thereof; atleast one rare earth metal selected from the group consisting of cerium,and yttrium, or mixtures thereof; and at least one transition metalcompound comprising iron, and manganese, or mixtures thereof, andproviding for operating of the diesel engine by burning the fuel over asufficient period of time to produce exhaust gases and achieve asustained reduction in unburned hydrocarbons and carbon monoxide.
 2. Themethod of claim 1, wherein the fuel borne catalyst comprises about 1 toabout 10 ppm of the at least one rare earth metal.
 3. The method ofclaim 1, wherein the fuel borne catalyst comprises about 0.5 ppm of theplatinum group metal composition.
 4. The method of claim 1, wherein thefuel borne catalyst comprises about 1 to about 10 ppm of the at leastone transition metal compound.
 5. The method of claim 1, wherein totalconcentration of the at least one rare earth metal, the platinum groupmetal composition, and the at least one transition metal compound isless than about 15 ppm.
 6. The method of claim 1, wherein the fuel bornecatalyst further comprises less than about 3 ppm of at least onematerial selected from the group consisting of silver, vanadium, andpalladium, or mixtures thereof.
 7. The method of claim 1, wherein thefuel borne catalyst further comprises less than about 3 ppm of at leastone material selected from the group consisting of calcium, andstrontium, or mixtures thereof.
 8. The method of claim 1, wherein thefuel borne catalyst further comprises less than about 3 ppm of at leastone material selected from the group consisting of sodium, and lithiumor mixtures thereof.
 9. The method of claim 1, wherein the at least onerare earth metal is fuel soluble.
 10. The method of claim 1, wherein theat least one fuel soluble transition metal compound is fuel soluble. 11.The method of claim 1, wherein the platinum group metal composition isfuel soluble.
 12. A method for improving operation of a diesel engine bylowering emissions of unburned hydrocarbons and carbon monoxide, themethod comprising the steps of: providing for a presence of a dieselfuel and combustion air; providing a fuel borne catalyst comprising aplatinum group metal composition comprising at least one materialselected from the group consisting of platinum, and palladium, ormixtures thereof, at least one rare earth metal selected from the groupconsisting of cerium, and yttrium, or mixtures thereof, and at least onetransition metal compound comprising iron, and manganese, or mixturesthereof; providing for combusting of the fuel in a diesel engine toproduce exhaust gases; and, providing for directing of exhaust gasesinto an exhaust system; wherein the fuel borne catalyst is introducedinto the fuel, the exhaust gases or the combustion air, in amountseffective to provide the fuel borne catalyst in the exhaust system at alevel of up to 1 ppm based on a volume of fuel burned to produce theexhaust gases.
 13. The method of claim 12, further comprising the stepof: providing at least one filter comprising at least one materialselected from the group consisting of platinum, palladium or mixturesthereof, and having a particle size less than about 40 nm.
 14. Themethod of claim 12, wherein the fuel borne catalyst comprises about 1 toabout 10 ppm of the at least one rare earth metal.
 15. The method ofclaim 12, wherein the fuel borne catalyst comprises about 0.5 ppm of theplatinum group metal composition.
 16. The method of claim 12, whereinthe fuel borne catalyst comprises about 1 to about 10 ppm of the atleast one transition metal compound.
 17. The method of claim 12, whereintotal concentration of the at least one rare earth metal, the platinumgroup metal composition, and the at least one transition metal compoundis less than about 15 ppm.
 18. The method of claim 12, wherein the fuelborne catalyst further comprises less than 3 ppm of at least onematerial selected from the group consisting of silver, vanadium, andpalladium, or mixtures thereof.
 19. The method of claim 12, wherein thefuel borne catalyst further comprises less than 3 ppm of at least onematerial selected from the group consisting of calcium, and strontium,or mixtures thereof.
 20. The method of claim 12, wherein the fuel bornecatalyst further comprises less than 3 ppm of at least one materialselected from the group consisting of sodium, and lithium, or mixturesthereof.
 21. The method of claim 12, wherein the at least one rare earthmetal is fuel soluble.
 22. The method of claim 12, wherein the at leastone transition metal compound is fuel soluble.
 23. The method of claim12, wherein the platinum group metal composition is fuel soluble.